The Stimulus Bill signed in 2009 by President Obama improves the tax credit and removes any cap from the incentive. A homeowner is no longer limited, and may collect the full 30% of the installed system cost as a tax credit for systems that are installed between January 1, 2009 and December 31, 2016.

Ground source heat pumps (GSHPs) are electrically powered systems that tap the stored energy of the greatest solar collector in existence: the earth. These systems use the earth's relatively constant temperature to provide heating, cooling, and hot water for homes and commercial buildings.